Combustion method with controlled fuel mixing

ABSTRACT

New combustors, and methods of operating same, which produce lower emissions, particularly lower emissions of nitrogen oxides.

United States Patent 1191 Schirmer et al.

COMBUSTION METHOD WITH CONTROLLED FUEL MIXING Inventors: Robert M.Schirmer; Ellsworth H. Fromm, both of Bartlesville, Okla.

Assignee: Phillips Petroleum, Bartlesville,

Okla. I

Filed: Dec.. 15, 1971 Appl. No.: 208,137

US. Cl 60/39.06, 60/3974, 431/10 Int. Cl. F02c 7/36 Field of Search60/3906, 39.69, 39.65, 60/3974 R; 431/10 References Cited UNlTED STATESPATENTS 1/1954 Whitelaw 60/3971 June 28, 1974 Ogilvie.'. 60/3974 RSchirmer.... 60/3906 Hopkins 60/3969 Helmrich 60/3974 R Ryberg et a1.60/3965 Warren 60/D1G. 10

Primary ExaminerCar1ton R. Croyle Assistant Examiner-Warren OlsenABSTRACT New combustors, and methods of operating same, which producelower emissions, particularly lower emissions of nitrogen oxides.

5 Claims, 10 Drawing Figures FUEL FIG. 5

SHEEIEUFS E u a FUEL AIR

FIG. 3

INVENTORS R. M. SCH IRMER E.H. FROMM ATTORNEYS PAIENTEDJum 1am SHEET 4BF 5 ill 1 JmDm O O O INVENTORS R M SCHIRMER E.H. FROMM BY 3 l /pm,

ATTORNEYS PATENTEDmza 1914 SHEET 5 OF 5 FIG. 7

INVENTORS R.M. SCHIRMER E.H. FROMM Q WM A T TORNEVS COMBUSTION METHODWITH CONTROLLED "FUEL MIXING This invention relates to improved gasturbine combustors and methods of operating same.

Air pollution has become a major problem in the United States and otherhighly industrialized countries of the world. Consequently, the controland/or reduction of said pollution has become the object of majorresearch and development effort by both governmental and nongovernmentalagencies. Combustion of fossil fuel is a primary source of saidpollution. It has been alleged, and there is supporting evidence, thatautomobiles employing conventional piston-type engines are a majorcontributor to said pollution. Vehicle emission standards have been setby the United States Environmental Protection Agency which aresufficiently ,restrictive to cause automobile manufacturers to consideremploying alternate engines instead of the conventional piston engine.

The gas turbine engine is being given serious consideration as analternate engine. However, insofar as we presently known, there is nopublished information disclosing realistic and/or practical combustorswhich can be operated at conditions typical of those existing in highperformance engines, and which will have emission levels meeting orreasonably approaching the standards set by said United StatesEnvironmental Protection Agency. This is particularly true with respectto nitrogen oxides emissions.

Thus, there is a need for a combustor of practical and/or realisticdesign which can be operated in a manner such that the emissionstherefrom will meet said Thus, according tothe invention, there isprovided a combustor comprising, in combination: a flame tube; air inletmeans for introducing a swirling stream of air into the upstream endportion of said flame tube; and fuel inlet means for introducing astream of fuel into said flame tube in a direction which is from tangentto less than perpendicular, but non-parallel, to the periphery of saidstream of air.

Further according to the invention, there is provided a method forreducing the amount of nitrogen oxides formed in the combustion of afuel in a combustor, which method comprises introducing a swirlingstream of air into the upstream end portion of a combustion zone;forming and introducing an annular stratum of said fuel around saidstream of air and in a direction which is from tangent to less thanperpendicular, but

non-parallel, to the periphery of said stream of air so as FIG. 2 is across section taken along the line 22 of FIG. 1.

FIGS. 3, 5, and 6 are views in cross section of the flame tube portionof other combustors in accordance with the invention. The outer housingor casing and other elements of these combustors is substantially likethat shown in FIG. 1.

FIG. 4 is a view in cross section taken along the lines 44 of FIG. 3.

FIG. 7 is a cross section along the line 77 of FIG. 3.

FIGS. 8 and 9 are views in cross section of other closure members ordome members which can be employed with the flame tubes of thecombustors described herein.

Referring now to the drawings wherein like reference numerals areemployed to denote like elements, the invention will be more fullyexplained. In FIG. 1 there is illustrated a combustor in accordance withthe invention, denoted generally by the reference numeral 10, whichcomprises a flame tube 12. Said flame tube 12 is open at its downstreamend, as shown, for communication with a conduit leading to a turbine orother utilization of the combustion gases. A closure member, designatedgenerally by the reference numeral 14, is provided for closing theupstream end of said flame tube. Said closure member can be fabricatedintegrally, i.e., as one element, if desired. However, it is presentlypreferred to fabricate said closure member 14 as two or more elements,e.g., an upstream element 16 and a downstream element 18. An'outercasing 20 is disposed concentrically around said flame tube 12 and saidclosure member 14, and spaced apart therefrom to form an annular chamber22 around said flame tube and said closure member. Said annular chamber22 is closed at its downstream end by any suitable means such as thatillustrated. Suitable flange members, as illustrated, are provided atthe downstream end of said flame tube 12 and outer housing 20 formounting same and connecting same to a conduit leading to a turbine orother utilization of the combustion gases from the combustor. Similarly,suitable flange members are provided at the upstream end of said flametube 12 and said outer housing 20 for mounting same and connecting sameto a conduit 24 which leads from a compressor or other source of air.While not shown in the drawing, it will be understood that suitablesupport members are employed for supporting said flame tube 12 and saidclosure member 14 in the outer housing 20 and said upstream end flangemembers. Said supporting members have been omitted so as to simplify thedrawing.

A generally cylindrical swirl chamber 26 is formed in said upstreamelement 16 of closure member 14. The downstream end of said swirlchamber 26 is in open communication with the upstream end of said flametube 12. A first air inlet means is provided for introducing a swirlingmass of air into the upstream end portion of said swirl chamber 26 andthen into the upstream end of said flame tuabe. As illustrated in FIGS.1 and 2, said air inlet means comprises a plurality of air conduits 28extending into said swirl chamber 26 tangentially with respect to theinner wall thereof. Said conduits 28 extend from said annular chamber 22into said swirl chamber 26.

A fuel inlet means is provided for introducing a stream of fuel in adirection which is from tangent to less than perpendicular, butnon-parallel, to the periphcry of said stream of air. As illustrated inFIGS. land 2, said fuel inlet means comprises a fuel conduit 30 leadingfrom a source of fuel, communicating with a passageway 32, which in turncommunicates with fuel passageway 34 whichis formed by an inner wall ofsaid downstream element 18 of closure member 14 and the downstream endwall of said upstream element 16 of closure member 14. It will be notedthat the inner wall of said downstream element is spaced apart from andis complementary in shape to the downstream end wall of said upstreamelement 16. The direction of the exit portion of said fuel passageway 34can be varied over a range which is intermediate or between tangent andperpendicular, but non-parallel, to the periphery of the stream of airexiting from swirl chamber 26. Varying the direction of the exit portionof fuel passageway 34 provides one means or method for controlling thedegree of mixing between the fuel stream and said air stream at theinterface therebetween. As illustrated in FIG. I, the directionof theexit portion of fuel passageway 34 forms an angle of approximately 45with respect to the periphery of the air exiting from swirl chamber 26.Generally speaking, in most instances, it

will be desired that the exit portion of said fuel passageway 34 has adirection which forms an angle within the range of from about l to about75, preferably about 30 to about 60 with respect to the periphery of thestream of air exiting from swirl chamber 26; In most instances, it willbe preferred that the fuel from fuel passageway 34 be introduced in agenerally downstream direction. However, it is within the scope of theinvention to introduce said fuel in an upstream direction. Shim 36provides means for varying the width of said fuel passageway 34. Anyother suitable means, such as threads provided onthe walls of upstreamelement 16 and downstream element 18, can be provided for varying thewidth of said fuel passage 34. As will be understood by those skilled'inthe art in view of this disclosure, the shape of the upstream inner wallof said downstream element 18 and the shape of the downstream end wallof said upstream element 16 can be changed, but maintained complementarywith respect to each other, so as to accommodate the above-describedchanges in direction and width of said fuel passageway 34.

A plurality of openings 38 is provided at a first station in thedownstream portion of said flame tube 12 for admitting a second streamof air into said flametube from said annular chamber 22. In thecombustor of the invention illustrated in FIG.- 1, said second stream ofair will principally comprise .quench air for quenching the combustionproducts before passing same on to the turbine.

Referring now to FIG. 3, there is illustrated the flame tube portion andclosure member therefor 'of another combustor in accordance with theinvention. It will be understood that the complete combustor willcomprise an outer housing or casing and suitable flange memberssubstantially as illustrated in FIG. 1. The flame tube 12 ofthecombustor of FlG..3 is substantially like flame tube 12 of FIG. I. Aclosure member 40 is mounted on the upstream end of said flame tube 12in any suitable manner so as to close the upstream end of said flametube except for the openings provided in said closure member. Agenerally cylindrical swirl chamber 42 is formed in said closure member40. The downstream end of said swirl chamber is in open communitube 12.As illustrated in FIGS. 3 and 4, said air inlet means comprises aplurality of air conduits 44 extending into said swirl chamber 42tangentially with respect to the inner wall thereof. Said conduits 44extend from an annular space 22, similarly as in FIG. 1. The fuel inlet'means in the combustor of FIG. 3 comprises a fuel supply conduit 46which is in communication with three fuel passageways 48, which in turnis in communication with an annular fuel passageway 51 formed in thedownstream end portion of said closure member 40. A plurality of fuelconduits 49 extend from said passageway 51 into a recess 50, also formedin the downstream end portion of said closure member, tangentially withrespect to the inner wall of said recess. As illustrated in FIGS. 3 and4, said air inlet conduits 44 are adapted to introduce air tangentiallyinto swirl chamber'42 in a clockwise direction (when lookingdownstream), and said fuel inlet conduits 49 in FIG. 7 are adapted tointroduce fuel tangentially into said recess 50 in a counterclockwisedirection. This is a presently preferred arrangement in one embodimentof the invention. However, it is within the scope of the invention toreverse the directions of said air inlet conduits 44 and said fuel inletconduits 49, or to have the directions of both said air inlet conduitsand said fuel inlet conduits the same, e.g., both clockwise or bothcounterclockwise.

Referring now to FIG. 5, there is illustrated the flame --tube portionand closure member therefor of another combustor in accordance with theinvention. The flame tube 52 of the combustor illustrated in FIG. 5 issubstantially like flame tube 12 in FIG. 1 except that the series of airinlet openings 38 has been moved in an upstream direction and a secondplurality of openings 54 has been provided at a second station in thedownstream portion of said flame tube 52, spaced apart from anddownstream from said first plurality of openings 38, for admitting asecond stream of air into the interior of said flame tube for an annularchamber 22 like that shown in FIG. 1 when an outer housing or casing isprovided around said flame tube. Closure member 14 for flame tube 52 islike closure member 14 in FIG. 1.

Referring now'to FIG. 6, there is illustrated the flame tube portion andclosure member therefor of another combustor in accordance with theinvention. The flame tube 56 of the combustor of FIG. 6 is like flametube 12 of FIG. 3 except that said flame tube 56 has been lengthened anda second plurality of openings 54 has been provided at a second stationin the downstream portion of said flame tube, downstream from and spacedapart from said first plurality of openings 38, for admitting a secondstream of air into the interior of said flame tube 56 from an annularspace like annular space 22 when an outer housing or casing is providedaround said flame tube, as in FIG. 1. Closure member 40 in FIG. 6 islike closure member 40 in FIG. 3.

Referring now to FIGS. 8 and 9, there are illustrated other types ofclosure members which can be employed with the flame tubes of thecombustors described above. In FIG. 8 closure member 78 is similar toclosure member 40 of FIG. 3. The principal difference is that in closuremember 78 a conduit means 80 is provided which extends through saidclosure member 78 into communication with the upstream end portion offlame tube 12, for example. At leastone swirl vane 82 is positioned insaid conduit means 80 for imparting a swirling motion to the air passingthrough said conduit means 80. In FIG. 9, closure member 84 is similarto closure member 14 of FIG. 1. The principal difference is thatinclosure member 84 an annular conduit means 88 is provided which extendsthrough the body of said closure member84 into open communication withthe upstream end of the flame tube 12, for example'At least one swirlvane 90 is provided in said conduit means 88 for imparting a swirlingmotion to the air passing through said conduit 88.

In the drawings certain closure members have been employed with certainflame tubes. However, it will be understood that the combustors of theinvention are entering saidswirl chamber and exiting therefrom. Thisswirling motion creates a strong vortex-action resulting in a reversecirculation of hot gases within flame tube 12 upstream toward said swirlchamber 26 during operation of the combustor.

A stream of fuel, preferably prevaporized, is admitted via conduit 30,passageway 32, and fuel passageway 34. Fuel exiting from fuel passageway34 is formed into an annular stratum around the swirling stream of airexiting from swirl chamber 26. This method of introducing fuel and aireffects a controlled mixing of said fuel and air at the interfacetherebetween. Initial contact of said fuel and air occurs upon the exitof said air from said swirl chamber 26. Immediately after said initialcontact the fuel and air streams (partially mixed at said interface) areexpanded, in a uniform and graduated manner during passage of said fueland air through the flared portion of member 18, from the volume thereofin the region of said initial contact to the volume of said combustionchamber at a point in said flame tube downstream from said initialcontact. Said expansion of fuel and air thus takes place during at leasta portion of the mixing of said fuel and said air. The resulting mixtureof fuel and air is burned and combustion gases exit the downstream endof flame. tube 12. A second stream of air, comprising quench airprincipally, is admitted to the interior of flame tube 12 from annularspace 22 via inlet openings 38 in the downstream portion of said flametube.

In one presently preferred method of operating the combustor of FIG. 3,the method of operation is similar to that described above for thecombustor of FIG. 1. A stream of air is admitted to swirl chamber 42 viatangential inlet conduits 44 which impart a helical or swirling motionto said air. A stream of fuel, preferably prevaporized, is admitted viaconduit 46, fuel passageways 48, and tangential fuel conduits 49 intorecess 50 formed at the downstream end of said closure member 40. Saidfuel is thus formed into an annular stratum around the swirling streamof air exiting from swirl chamber 42. This method of introducing fueland air also effects controlled mixing of said fuel and air at theinterface therebetween.

In one presently preferred method of operating the combustor of FIG. 5,the operation is similar to that described above for the combustor ofFIG. 1. A principal difference is that in addition to the stream of airadmitted from annular space 22 via openings 38 into the interior offlame tube 52, another stream of air is admitted to the interior of saidflame tube via openings 54. The amounts of the various streams of airadmitted through tangential openings 28, openings 38, and openings 54can be controlled by varying and/or correlating the size of saidopeningsrelative to each other as described further hereinafter inconnection with the examples.

The method of operation of the combustor of FIG. 6

is substantially like that described above for FIG. 5,

- taking into consideration that closure member 40 in FIG. 6 is likeclosure member in FIG. 3.

The following examples will serve to further illustrate the invention.

EXAMPLES A series of test runs was made employing combustors of theinvention described herein, and a typical standard or prior artcombustor as a control combustor. The same fuel was used in all of saidtest runs. Properties of said fuel are set forth in Table I below.Design details of the combustors of the invention are set forth in TableII below. Said design details, e.g., dimensions, are given by way ofillustration only and are not to be construed as limiting the invention.Said dimensions can be varied within wide limits so long as the improvedresults of the invention are obtained. For example, the

formation of nitrogen oxides in a combustion zone is an equilibriumreaction. Thus, in designing a combustion zone, attention should begiven to the size thereof so as to avoid unduly increasing the residencetime therein. It is desirable that said residence time not be longenough to permit the reactions involved in the formation of nitrogenoxides to attain equilibrium. In said Table II thecombustors have beenidentified by a number which is the same as the figure number of whichthey are illustrated.

Said control combustor basically embodies the principal features ofcombustors employed in modern aircraft-turbine engines. It is astraight-through can-type combustor employing fuel atomization by asingle simplex-type nozzle. The combustor liner was fabricated from2-inch pipe, with added internal deflector skirts for air film coolingof surfaces exposed to the flame. Exhaust emissions from this combustor,when operated at comparable conditions for combustion, are in generalagreement with measurements presently available from several differentgas turbine engines. Said control combustor had dimensions generallycomparable to the above described combustors of the invention.

Each of said combustors of the invention and said control combustor wasrun at 12 test points or conditions, i.e., 12 different combinations ofinlet-air temperature, combustor pressure, flow velocity, and heat inputrate. Test points or conditions 1 to 6 simulate idling conditions, andtest points 7 to 12 simulate maximum power conditions. The combustors ofthe invention were run using prevaporized fuel. The control combustorwas run using atomized fuel. Analyses for content of nitrogen oxides(reported as NO), carbon Volume, cubic inches 37.751

' monoxide and hydrocarbons (reported as carbon) in the combustorexhaust gases were made at each test' condition for each combustor. Eachpollutant measured is reported in terms of pounds per 1000 pounds offuel fed to the combustor. The results from test conditions l to 6 areset forth in Table 111 below. The results from test conditions 7 to 12are set forth in Table IV below.

TABLE I PHYSICAL AND CHEMICAL PROPERTIES OF TEST FUEL Philjet A-SO ASTMDistillation. F

Initial Boiling Point 340 15 5 vol evaporated 359 10 vol evaporated 362vol 7: evaporated 371 vol it evaporated 376 vol 7c evaporated 387 vol 7:evaporated 398 I vol 7: evaporated 409 20 vol evaporated 424 volevaporated 442 vol evaporated 461 vol 7:. evaporated 474 End Point 496Residue. vol 72 0.8 I Loss. vol 7: 0.0 25 Gravity, degrees APl I 46.6Density, lbs/gal 6.615 Heat of Combustion. net, Btu/lb 18,670 HydrogenContent, wt 14.2 Smoke Point, mm 27.2 Sulfur, wt 71' 0.001 Gum, mg/ ml0.0 30 Composition,.vol 7c Paraffins 52.8 Cycloparaffins 34.5 Olefins0.1 Aromatics 12.6

Formula (calculated) (C H 35 Stoichiometric Fuel/Air Ratio. lb/lb 0.0676

TABLE 11 COMBUSTOR DESIGN Combustor Number Variable l 3 5 6 ClosureMember (14 or 40) Air lnlet Diameter, inches 0.875 1.250 0.875 1.250lnlet Type Tangent Tangent Tangent Tangent Hole Diameter, inches 0.2500.281 0.250 0.281

Number of Holes 6 6 6 6 Total Hole Area, square inches 0.295 0.373 0.2950.373 percent Total Combustor Hole Area 10.554 12.983 5.571 6.942 FuelSlot. inches I 0.005 0.005 Fuel Tube Diameter, inches '12-0.062 120.062

Exit Type Tangent Tangent Flame Tube First Station (38) Hole Diameter,inches 5/16 1* 5ll6 l 5/16 1 5/16X1 Total Number of Holes 8 8 8 8 TotalHole Aremsquare inches 2.500 2.500 2.500 2500 Percent Total CombustorHole Area 89.446 87.017 47.214 46.528 Second Station (54) I HoleDiameter, inches 5/l6 1 5/16X1 Total Number of Holes 8 8 Total HoleArea. square inches 2.500 2.500 Percent Total Combustor Hole area 47.21446.528

Total (ombustor Hole Area, square inches I 2.795 2.873 5.295 I 5.373Combustor Cross Section Area, square inches 3.355 3.355 3.355 I 3.355Percent Cross Sectional Area 83.293 85.616 157.777 160.101

Combustor Inside Diameter, inches 2.067 2.067 2.067 I 2.067 Primary ZoneLength, inches 7.125 I 6.125 4.625 6.125

Volume, cubic inches 23.909 20.554 15.520 20.554 Comhustor Length.inches 11.250 1.0.250 11.250 12.750 34.395 37.751 42.784

' Holes are 5/16 inch diameter all ends; slots are 1 inch long.

Test Conditions lbs/I000 lbs Fuel TABLE lll COMPARISON OF EMISSIONS FROMCOMBUSTORS AT IDLE CONDITIONS Comhustor Operating Variables TemperatureInlet Air. F. Pressure. in. Hg abs. Velocity. Cold Flow, ft/scc.Hcablnput RutmBtu/lb Air NITROGEN OXIDES o 1 N C 3.

Combustors Control Com hustor Combustor Comhuslor Comhustor Comhustorlbs/I000 lbs Fuel CARBON MONOXIDE Comhustors Control Com hustorComhustor Comhustor Combustor Combustor lbs/ I .000 lbs FuelHYDROCARBONS I I I0 400 300 IIOO I I0 400 225 Test Conditions I I00 I100 1 10 I 10 250 400 300 I50 lbs/I000 lbs Fuel TABLE IV 1 r00 100 1 10l 10 250 250 22s Cornbustor Combustor COMPARISON OF EMISSIONS FROMCOMBUSTORS AT MAXIMUM POWER CONDITIONS Combustor Operating VariablesTemperature. lnlct Air, F.

Pressure, in Hg ahs. Velocity. Cold Flow. ft/scc Hunt-Input Rate.Btu/Ib.Air

Combustors No. Control Combustor Comhustor NITROGEN OXIDES CombustorComhustur lbs/ I 000 lbs Fuel Comhustor Comhustor Combustor lhs/I000 lbsFuel HY DROCARBONS Comhustors Control (om buslor Comhustor ComhustorComhustor Comhustor Referring to the above Tables III and IV, the datathere given clearly show that allthe combustors of the invention gaveresults superior to the results obtained with the control combustor.Combustor No. 1 gave outstanding results at substantially all testconditions with respect to nitrogen oxides emissions, the pollutant mostdifficult to control. Said data also show that all the combustors of theinvention can be operated at idle conditions to give not more than about1.8 pounds of nitrogen oxide emissions per 1000 pounds of fuel burned,and not more than about pounds of nitrogen oxide emissions per 1000pounds of fuel burned at maximum power conditions. Such operatingconditions would be preferred operating conditions.

Under some of the test conditions, combustors 1 and 3 tend to give highcarbon monoxide emission. This situation was alleviated by combustors 5and 6 which maintained low levels of nitrogen oxide emissions whilereducing the carbon monoxide emissions. It should be noted that thisresult was obtained by changes which are completely contra to currentconcepts of combustor design. In the operation of combustors 5 and 6 thetotal amount of air to the combustor was maintained constant, e.g., thesame as to combustors 1 and 3. However, the amount of air to the primarycombustion zone of combustors 5 and 6 was decreased by increasing theamount of secondary and/or quench air admitted to the downstream portionof the flame tube. This was accomplished by adding the second set ofinlet slots 54 downstream from the first set of inlet slots 38. This hadthe effect of enriching the primary combustion zone, which wouldincrease carbon monoxide emissions from atypical prior art combustor.

The operation of saidcombustors 5 and 6 embodies presently preferredmethods in accordance with the invention. In accordance with saidmethods the volume of air utilized as primary air is decreased in anamount sufficient to enrich the fuel to air ratio in the primarycombustion zone, and the volume of the remaining air which is introduceddownstream of the primary com.- bustion zone is increased. Saidremaining stream of air of increased volume is divided into a firststream comprising secondaryv air and a second stream comprising quenchair. Said first stream comprising secondary air is introduced into'afirst region, e.g., slots 38, downstream from'the primary combustionzone and said stream comprising quench air is introduced into the flametube of the combustor at a second region, e.g., slots 54, spaced apartfrom and downstream from said first region. In practicing said preferredmethods of the invention, good results have been obtained when thevolume of the stream of primary air is decreased by an amount within therange of from about 25 to about 75 per cent'by volume of'the volume'ofprimary air at which the combustor would normally be operated. The

remainder of the air to the combustor is then divided into a streamcomprising from about 70 to about 30 volume per cent thereof and used assaid stream comprising secondary air, and a stream comprising from about30 to about 70 volume percent of said remaining stream of air and usedas said stream comprising quench air.

In the examples, the fuel to the combustors of the inventionwasprevaporized. However, the invention is For comparison purposes, all theruns set forth in the above examples were carried out under theconditions of inlet air temperature, combustor pressure, flow velocity,and heat input rate set forth in Tables lll and IV.

The invention is not limited to the values there given for saidvariables. It is within the scope of the invention to operate thecombustors of the invention under any conditions which give the improvedresults of the invention. For example, it is within the scope of theinvention to operate said combustors at inlet air tempera tures withinthe range of from ambient temperatures or lower to about l500F. orhigher; at combustor pressures within the range of from about 1 to about40 atmospheres or higher; at flow velocities within the range of fromabout 1 to about 500 ft. per second or higher; and at heat input rateswithin the range of from about 30 to about 1200 BTU per second of air.

The term air" is employed generically herein and in the claims, forconvenience, to include air and other combustion supporting gases.

While the invention has been described, in some instances, withparticular reference to combustors employed in combination with gasturbine engines, the invention is not limited thereto. The combustors ofthe invention have utility in other application, e.g., boilers.

While certain embodiments of the invention have been described forillustrative purposes, the invention obviously is not limited thereto.Various other modifications will beapparent to those skilled in the artin view'of this disclosure. Such modifications are within the spirit andscope of the invention.

ides forrned in the combustion of a fuel in a combustor,

which method comprises:

introducing a swirling stream of air into the upstream end portion of acombustion zone as the sole stream of primary air introduced into saidcombustion zone;

forming and introducing an annular stratum of said fuel around saidstream of air by introducing said fuel in a direction toward and whichis from tangent to less than perpendicular, but non-parallel, to theperiphery of said stream of air so as to effect controlled mixing ofsaid fuel and air at the interface therebetween to produce an annularfuel-air mixture;

passing said fuel-air mixture into said combustion I zone asthe solefuel and air supplied to the upstream portion of said combustion zone;and burning said fuel.

2. A'method according to claim 1 wherein the combustion gases producedin said combustion zone by burning the thus mixed fuel and air andexiting from said combustion zonehave a nitrogen oxides content,calculated as N0, of not more than 5 pounds per 1000 pounds of saidfuelburned.

3. A method according to claim 1 wherein said fuel and said air areexpanded during at least a portion of said mixing thereof, and saidexpansion of said fuel and said air is initiated immediately after theinitial contact at said interface therebetween.

4. A method according to claim 3 wherein:

said stream of air is initially introduced into a swirl zone. having adiameter less than the diameter of said combustion zone;

said initial contact between said fuel and said air oc- 14' saidcombustion chamber downstream from said initial contact. V

5. A method according to claim 2 wherein a second stream of aircomprising quench air is introduced into said combustion zone downstreamfrom the point of introduction of said swirling stream of air.

1. A method for reducing the amount of nitrogen oxides formed in thecombustion of a fuel in a combustor, which method comprises: introducinga swirling stream of air into the upstream end portion of a combustionzone as the sole stream of primary air introduced into said combustionzone; forming and introducing an annular stratum of said fuel aroundsaid stream of air by introducing said fuel in a direction toward andwhich is from tangent to less than perpendicular, but non-parallel, tothe periphery of said stream of air so as to effect controlled mixing ofsaid fuel and air at the interface therebetween to produce an annularfuel-air mixture; passing said fuel-air mixture into said combustionzone as the sole fuel and air supplied to the upstream portion of saidcombustion zone; and burning said fuel.
 2. A method according to claim 1wherein the combustion gases produced in said combustion zone by burningthe thus mixed fuel and air and exiting from said combustion zone have anitrogen oxides content, calculated as NO, of not more than 5 pounds per1000 pounds of said fuel burned.
 3. A method according to claim 1wherein said fuel and said air are expanded during at least a portion ofsaid mixing thereof, and said expansion of said fuel and said air isinitiated immediately after the initial contact at said interfacetherebetween.
 4. A method according to claim 3 wherein: said stream ofair is initially introduced into a swirl zone having a diameter lessthan the diameter of said combustion zone; said initial contact betweensaid fuel and said air occurs upon the exit of said air from said swirlzone; and said expansion of said fuel and said air occurs in a uniformand graduated manner from the volume thereof in the region of saidinitial contact to the volume of said combustion chamber at a point insaid combustion chamber downstream from said initial contact.
 5. Amethod according to claim 2 wherein a second stream of air comprisingquench air is introduced into said combustion zone downstream from thepoint of introduction of said swirling stream of air.